Use mass_dns to do forward lookups. Fixes #1451

TargetGroup.h

@@ -70,22 +70,19 @@
 #include <cstddef>
 
 class NetBlock;
+class HostGroupState;
 
 class TargetGroup {
 public:
-  NetBlock *netblock;
-
-  TargetGroup() {
-    this->netblock = NULL;
-  }
+  TargetGroup() : netblocks() {}
 
   ~TargetGroup();
 
   /* Initializes (or reinitializes) the object with a new expression,
      such as 192.168.0.0/16 , 10.1.0-5.1-254 , or
      fe80::202:e3ff:fe14:1102 .  The af parameter is AF_INET or
-     AF_INET6 Returns 0 for success */
-  int parse_expr(const char *target_expr, int af);
+     AF_INET6. */
+  bool load_expressions(HostGroupState *hs, int af);
   /* Grab the next host from this expression (if any).  Returns 0 and
      fills in ss if successful.  ss must point to a pre-allocated
      sockaddr_storage structure */